Manufacturing process using microwave for thermal debinding

ABSTRACT

A manufacturing process using microwave for thermal debinding according to the invention is mainly applied in manufacturing process of powder metallurgy. Wherein, metal powder is mixed polymer materials such as adhesives, fillings or lubricants, and a body is formed by means of molding, forging, extrusion, injection or scraping. The body to be debinded is placed in a microwave environment in an exposed manner or covered with powder, and power and work time of microwave are set for rapidly heating and debinding the body. The manufacturing process according to the invention is capable of accelerating manufacturing procedure, economizing production cost, reducing defects, quickly drying and rapidly removing polymer materials.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The invention relates to a manufacturing process using microwave for thermal debinding, and more particularly, to a manufacturing process using microwave for thermal debinding applied in powder metallurgy. Appropriate microwave power and reaction time are utilized for heating and rapidly debinding a body, thereby minimizing defects of finished products of powder metallurgy, economizing equipment and resource costs, quickly drying and rapidly removing polymer materials namely adhesives, fillings and lubricants.

(b) Description of the Prior Art

In common manufacturing processes of powder metallurgy, in order to facilitate ceramic powder to cast into bodies more easily, polymer materials are frequently added to the bodies as cast additives. Such type of cast additives includes adhesives, surfactants, fillings or lubricants. The cast additives are mixed with polymer materials for casting bodies that may be formed by methods such as molding, forging, extrusion, injection or scraping. Then the bodies are placed into furnaces for debinding as the next step.

Extrusions from ceramic powder possess properties of general plastic extrusions, and are materials that can be used with high efficiency. When extrusions from ceramic powder are adopted for products having complicated shapes in mass production, the products have relatively better microstructures because sizes thereof are evenly contracted. Therefore, the extruded products approach net shapes or near net shapes without requiring a great amount of subsequent processing, and thus significantly economizing production costs thereof by reducing processing expenses. However, the cast additives used come as high as 30 vol %, and defects incurred are prone to arise during removal of the polymer materials in the debinding process. To be more precise, the debinding process stands as a rather major manufacturing process.

In the present invention, issues like body casting, sintering, materials of powder, or ingredients of additives shall not be discussed. Instead, the invention is targeted at providing another processing method for the debinding step in the manufacturing process.

As described above, common debinding processes currently used include solvent debinding and thermal debinding, wherein:

-   -   1. Solvent debinding is implemented by the steps of dipping a         body into a solvent, and extracting dissolvable adhesives,         fillings, surfactants or lubricants from the body for forming         successive openings penetrating from an interior to an exterior         of a sample. Thus, subsequent heating is able to facilitate         exudation of residual adhesive in form of a gas or a liquid         through the openings. In addition, debinding efficiency is         increased while decreasing defects by pressurizing the solvent         to a supercritical state or heating the solvent into steams.         However, such means of solvent debinding brings forth         environmental and recycling issues and thus further increases         processing expenses thereof.     -   2. Thermal debinding is implemented by the steps of placing a         body into a furnace, and removing adhesives directly or after         solvent debinding. Only human-friendly gases that give no         environmental, recycling or human-hazardous issues like those in         the solvent debinding are produced, and therefore thermal         debinding is the most extensively applied debinding process.         Nevertheless, it is necessary to pre-heat the furnaces to a         temperature required for thermal debinding, meaning that time         and energy for pre-heating and energy consumed during         maintaining the heat yet sum up to considerable amounts of         money, and an efficiency problem often abstained by the         manufacturing process is resulted. Also, defects are prone to         occur during the time-consuming thermal debinding process, and         hence reforms with respect to the above shortcomings can yet be         advanced.

Furthermore, the modern times is an environmental-friendly era, especially regarding to uses and recycling of resources. It shall be taken into consideration that a chemical solvent, which is non-eco-friendly and is limited to a certain number of times to be used, is adopted for solvent debinding; and furnaces employed for thermal debinding are quite energy consuming. Therefore, it is a vital and urgent task as how to provide a processing technique for debinding capable of rapidly accomplishing the debinding process and reducing resource wastage, as well as being environmental-friendly.

With respect of the aforesaid shortcomings, domestic and international patent publications or related information are taken into reference. Referring to the Taiwan Patent Publication No. 333482, “Manufacturing Process for Carbon Chromium/Aluminum Oxide Ceramic Devices Having Complicated Shapes Using Extrusion Technique”, it is observed that several defects are derived from the debinding process thereof:

-   -   1. The furnaces are troublesome and time-consuming in lowering         the temperatures thereof. Production cost thereof can be reduced         and manufacturing efficiency thereof can be elevated if time for         heating from room temperature to a temperature required for         debinding and lowering temperature after debinding completed can         be shortened.     -   2. Energy cannot be concentrated entirely on a body. During         heating of a common furnace, a major part of energy is absorbed         through the furnace body and lost into the atmosphere, and thus         leaving as little as 30 percent of the original energy for         debinding the body. It is indeed uneconomical to waste such         great amounts of energy for merely achieving the purpose of         debinding.     -   3. Common furnaces take up large spaces for that they are         massive in volume and heavy in weight, and lack mobility so that         difficulties arise when moving such furnaces.     -   4. Furnaces have high equipment cost. Expense burdens and         maintenance fees thereof are unnecessarily increased. Also,         problems of heating bodies and heat-resistant materials are         easily caused by any contamination of adhesion decompositions in         the furnaces.     -   5. Chemical solvents are limited to certain expiration periods.         In solvent debinding, chemical extraction properties of chemical         solvents are inevitably lowered after having been used for a         period of time or when increasing the number of bodies. Besides,         expired chemical solvents may become another environmental         dilemma.     -   6. Defects are liable due to uneven temperature distribution in         conventional heating. When heating a sample by a resistor         heating body, heat energy is conducted to the sample by         conduction and convection. Not only temperature inside a furnace         but also temperature in and out of the sample is unevenly         distributed. As a result, defects such as breakage, deformation,         swelling and collapsing are produced in the thermal debinding         process. When using microwave for simultaneously heating         microwave-absorbent objects in the sample, for instance, polymer         materials and metal power, an equal temperature is maintained in         and out of the sample, and defects are then significantly         reduced.

In addition, referring to Taiwan Patent Publication No. 167524 disclosing a method for thermal processing unstable ceramics using microwave, a microwave technique is applied during the sintering process of ceramics. In this prior invention, a microwave acceptor is formed from an appropriate powder bed that is characterized with respect to heating, protection, deoxidization and thermal conductance as required. However, the characteristics are provided for the requirements of the “sintering” process of ceramics; that is, this prior invention confers nothing upon the “debinding” process of ceramic bodies before the sintering process. Therefore, the shortcomings of the aforesaid debinding means (solvent debinding and thermal debinding) are yet not resolved by the Taiwan Patent Publication No. 167524.

Conclusive from the above, as described by shortcomings and issues of the conventional debinding means, the handling of the solvent used in solvent debinding are troublesome, uneconomical and non-eco-friendly, and furnaces adopted for thermal debinding are time-consuming for heating and temperature lowering. Therefore, it is a vital task of the invention as how to provide a manufacturing process capable of overcoming the prior disadvantages such as having high production and equipment cost, lack of mobility and being unable to concentrate energy.

SUMMARY OF THE INVENTION

The primary object of the invention is to provide a manufacturing process capable of accelerating production procedure, reducing production cost, rapidly drying and removing adhesives, fillings or lubricants. The manufacturing process is suitable for debinding of cast bodies after powder materials are mixed with adhesives, fillings or lubricants, and is able to avoid energy wastage in heating and temperature lowering as well as keeping away from being bulky in size.

Another object of the invention is to provide manufacturing equipment and method for elevating manufacturing efficiency by shortening the time of heating and temperature lowering. Microwave-absorbent medium therein can be repeatedly used for avoiding contamination of the environment. The manufacturing equipment and method accomplish energy saving purposes by concentrating energy, and therefore have excellences including low equipment cost and mobility for further reducing production cost and facilitating the moving thereof.

The invention is characterized that, when a body enters a debinding procedure, the body is placed in a microwave environment, and powder bed is adjusted and microwave reaction time is set for debinding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow chart of manufacturing process of powder metallurgy.

FIG. 2 shows a schematic diagram of the debinding procedure according to the invention.

FIG. 3 shows a schematic diagram of the sintering procedure according to the invention.

FIG. 4 shows a comparison table illustrating relative densities after sintering by the present invention and a prior art.

FIG. 5 shows comparison diagram illustrating time required for debinding in the present invention and a prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

To better understand the manufacturing process and functions of the present invention, descriptions shall be given with the accompanying drawings below.

Referring to FIG. 1, procedures of powder metallurgy are: a. forming a body, b. debinding, c. sintering, and d. finishing product. The invention is a manufacturing process using microwave for thermal debinding. When being applied in powder metallurgy, the invention comprises the steps of:

-   -   a. forming a body: powder of iron, nickel and copper is mixed         with a weight ratio of 90:6:4, and the mixture is then blended         with a mixture of low density polyethylene (LDPE), ethylene         vinyl acetate (EVA), paraffin wax (PW) and stearic acid (SA)         with a weight ratio of 12:12:61:15 at a temperature range         between 120 to 160° C. for forming a body 1; wherein the         aforesaid metal may be pure metals or alloys of iron (Fe),         titanium (Ti), copper (Cu), magnesium (Mg), nickel (Ni),         chromium (Cr) and manganese (Mn);     -   b. debinding: the body 1 to be debinded is placed into a carrier         3, and is directly debinded along with the carrier 3; or the         body 1 is first covered with a powder bed made of zirconium         oxide (ZrO₂), and then heated for debinding; wherein the powder         bed 2 is for maintaining shape of the body 1 and for preventing         contacts between individual bodies 1 when a number of the bodies         is more than one, and the powder bed 2 is aluminum oxide (Al₂O₃)         or a mixture of silicon oxide (SiO₂) and zirconium oxide (ZrO₂)         of any ratio;     -   c. sintering: a half-finished product 6 after debinding is         placed in a sintering furnace 5 and sintered; and     -   d. finishing product: normal procedure is used for lowering         temperature, and a finished product 7 is formed and taken out.

Referring to FIG. 2, the characteristics of the invention are that, the body 1 is placed in a microwave environment, which is a microwave oven 4 in this embodiment, and the body 1 is heated for debinding using microwave. Wherein, reaction time for microwave is set between 10 minutes and 15 hours, and power of microwave is between 30 to 2000W. During the debinding process, direct observations through a window 41 may be carried out for controlling results of the debinding process. The method of placing the body 1 into the microwave environment may be any of the following:

-   -   1. the body 1 is directly placed and exposed in the microwave         environment;     -   2. the body 1 is placed in the carrier 3, and put in the         microwave environment along with the carrier 3, wherein the         carrier 3 is a crucible in this embodiment;     -   3. the body 1 is placed in the carrier 3, entirely or partially         buried in the powder of the powder bed 2, and put in the         microwave environment altogether, wherein the powder of the         powder bed 2 is a microwave-absorbent medium.

Referring to FIG. 3, after debinding, the half-finished product 6 is continuously and directly heated to the sintering temperature in the microwave environment, and is placed into a sintering furnace having already reached the sintering temperature for obtaining the finished product 7. Or, the half-finished product 6 is remained in the microwave environment (the microwave 4), and is directly sintered using microwave for obtaining the finished product 7; time and resource required by gradual heating may then be conserved.

Using the technique provided by the manufacturing process using microwave for thermal debinding according to the invention, shortcomings existing in prior debinding methods including slow temperature rising and lowering, long manufacturing time, non-concentrated heating energy, uneconomical costs, bulky furnaces, lack of mobility, and unsatisfactory efficiency and non-eco-friendliness of solvents, are all effectively resolved. Through the manufacturing method according to the invention, effects of accelerating production procedure, decreasing defects, reducing production cost, and rapidly removing adhesives, fillings or lubricants are accomplished. The manufacturing process is especially suitable for the debinding step of cast bodies after powder materials are mixed with adhesives, fillings or lubricants.

The aforesaid polymer materials are adhesives, fillings or lubricants, and may be any from acrylic, ethyl cellulose, hydroxypropyl cellulose, polypropylene cellulose, polypropylene, polyacetal polymer, ethylene vinyl acetate, atactic polypropylene, sterene-butadienecpolymer, methyl cellulose, polyethylene, oxidized polyethylene, cellulose acetate, nylon, polystyrene, polybutylene, polysulfone, paraffin wax, mineral oil, vegetable oil, fatty acid, fatty alcohol, fatty ester, hydrocarbon wax, epoxy, polyphenylene, phenol, stearic acid, ester wax, oleic acid, diethyl phthalate, and formaldehyde.

It is of course to be understood that the embodiment described herein is merely illustrative of the principles of the invention and that a wide variety of modifications thereto may be effected by persons skilled in the art without departing from the spirit and scope of the invention as set forth in the following claims. 

1. A manufacturing process using microwave for thermal debinding comprising the steps of: a. forming a body from a mixture of metal powder and polymer materials; b. debinding the body using microwave heat; c. sintering the debinded half-finished product; and e. forming a sintered finished product after lowering temperature thereof; and the characteristics thereof being that, when the body enters the debinding procedure, the body is placed into a microwave environment, and is debinded after adjusting power and setting work time of microwave.
 2. The manufacturing process using microwave for thermal debinding according to claim 1, wherein the body is exposed in the microwave environment for debinding.
 3. The manufacturing process using microwave for thermal debinding according to claim 1, wherein the body is put into a crucible and debinded along with the crucible in the microwave environment.
 4. The manufacturing process using microwave for thermal debinding according to claim 1, wherein the body is put into a powder bed, covered by microwave-absorbent powder, and placed into the microwave environment.
 5. The manufacturing process using microwave for thermal debinding according to claim 1, wherein the debinded half-finished product is continuously and directly heated to a sintering temperature in the microwave environment, and then placed into a furnace having reached a sintering temperature.
 6. The manufacturing process using microwave for thermal debinding according to claim 1, wherein the debinded half-finished product is directly sintered using microwave in the microwave environment.
 7. The manufacturing process using microwave for thermal debinding according to claim 1, wherein the metal powder is made of a pure metal from or an alloy of iron (Fe), titanium (Ti), copper (Cu), magnesium (Mg), nickel (Ni), chromium (Cr) and manganese (Mn).
 8. The manufacturing process using microwave for thermal debinding according to claim 1, wherein the body is formed by means of molding, forging, extrusion, injection or scraping.
 9. The manufacturing process using microwave for thermal debinding according to claim 4, wherein the powder bed is made of a mixture of aluminum oxide (Al₂O₃) or a mixture of silicon oxide (SiO₂) and zirconium oxide (ZrO₂) of any ratio.
 10. The manufacturing process using microwave for thermal debinding according to claim 1, wherein the polymer materials are any from acrylic, ethyl cellulose, hydroxypropyl cellulose, polypropylene cellulose, polypropylene, polyacetal polymer, ethylene vinyl acetate, atactic polypropylene, sterene-butadienecpolymer, methyl cellulose, polyethylene, oxidized polyethylene, cellulose acetate, nylon, polystyrene, polybutylene, polysulfone, paraffin wax, mineral oil, vegetable oil, fatty acid, fatty alcohol, fatty ester, hydrocarbon wax, epoxy, polyphenylene, phenol, stearic acid, ester wax, oleic acid, diethyl phthalate, and formaldehyde. 